The present invention relates to fiber-optic communications networks, and more particularly, to optical amplifiers and other network equipment for optical communications networks having pump current limiting features.
Fiber-optic networks are used to support voice and data communications. In optical networks that use wavelength division multiplexing, multiple wavelengths of light are used to support multiple communications channels on a single fiber.
Optical amplifiers are used in fiber-optic networks to amplify optical signals. For example, optical amplifiers may be used to amplify optical data signals that have been subject to attenuation over fiber-optic paths. A typical amplifier may include erbium-doped fiber coils that are pumped with diode lasers. Raman amplifiers have also been investigated. Discrete Raman amplifiers may use coils of dispersion-compensating fiber to provide Raman gain. Distributed Raman amplifiers provide gain in the transmission fiber spans that are used to carry optical data signals between network nodes. Diode lasers may be used as Raman pumps for Raman amplifiers.
The diode lasers used as pumps in erbium-doped fiber amplifiers and Raman amplifiers have a maximum power capacity. If such lasers are driven too strongly, the maximum power capacity will be exceeded and the lasers will be damaged. In some amplifiers, lasers have been provided with back facet monitors to make real-time output power measurements. These measurements can be used to limit the maximum output powers of the lasers. Using back facet monitoring may not, always be desirable, however, due to challenges associated with achieving high measurement accuracy, low cost, and low complexity.
It is an object of the present invention to provide improved optical network equipment such as optical amplifiers in which laser diode pumps are operated at levels below those that might damage the pumps.
It is also an object of the present invention to provide optical network equipment such as optical amplifiers in which information on the ages of the pumps is used to estimate the maximum allowable drive current for the pumps.
These and other objects of the invention are accomplished in accordance with the present invention by providing optical amplifiers and other optical network equipment for use in fiber-optic communications links in fiber-optic networks. The fiber-optic links may be used to carry optical data signals associated with wavelength-division-multiplexing channels. The equipment may provide optical gain for the optical signals.
The optical gain may be provided by pumping fiber with laser diode pumps. Control units in the equipment may be used to keep track of pump age. As time elapses, the control unit may use information on age of the pumps to determine the maximum allowable drive currents for the pumps. The pumps may be driven as needed to produce desired currents, output powers, or gains in the equipment, provided that the maximum allowable drive currents are not exceeded. Pump age information may also be used in calibrating the operating currents for the lasers.